JP2006510068A - Fabrication of molding structure of LCD cell and mask therefor - Google Patents

Abstract

A method for forming a molding structure in a liquid crystal display cell is to apply a photosensitive layer (6) to a transistor plate (2) and to form a photosensitive layer in a photolithographic process using a gray gradation photomask (7, 21). Forming a molded structure. This mask comprises at least one region (8, 16, 18) of translucent material, the transparency of which depends on the optical band gap of the material.

Description

  The present invention relates to the manufacture of liquid crystal displays and their features. In particular, the present invention relates to a method of forming a shaped structure in a liquid crystal display (LCD) cell using a translucent mask.

  An example of such a LCD structure is a diffusely reflective pixel electrode as used in thin film transistor (TFT) reflective active matrix liquid crystal displays (reflective AMLCD). This is generally formed using an irregular topography, so that when covered with a reflective metal layer, usually aluminum or silver, the incident light is distributed over one surface of the LCD viewing area. Importantly, this dispersion is controlled to take into account the tradeoff between having a substantially wide viewing area and having the appropriate reflected light intensity within that viewing area. One known method for forming this irregular surface is to first apply a photosensitive layer to the TFT plate of AMLCD. This layer is then patterned by conventional photolithography and etching to form a number of microbumps on the surface of each electrode of the TFT plate. This results in a surface topography with islands with steep sides, which are then heated to cause reflow, providing a more curved surface topography, and the surface topography is covered with a reflective metal coating .

  In a more complex method of forming a diffusely reflective pixel electrode such as that disclosed in US Pat. No. 6,163,405, at least one slope is the surface of the pixel electrode on the TFT plate prior to forming the microbump. Incorporated. In this way, the light is reflected to a preferred viewing area that may not be perpendicular to the TFT plate. This type of tilted diffuse reflector is called a diffuse micro tilted reflector (DMSR).

  U.S. Patent No. 6,163,405 discloses several methods including photolithography to form such a sloped surface on the pixel electrode and to form irregular micro bumps thereon. The main method disclosed relates to the generation of irregular ridges of varying heights by using a single photomask many times as part of a photolithography multiple exposure shift method. The photomask is lined up on a mask that is UV opaque, except for a small UV transparent slot. The ultraviolet light is then directed through the mask to the photosensitive material layer applied to the pixel electrode. In positive photolithography, ultraviolet light is used to expose the photosensitive material and the exposed areas are removed during the development stage. Conversely, negative photolithography removes areas of the photosensitive material that were not irradiated with ultraviolet light during the development stage.

  After UV irradiation of a certain UV intensity, the mask with the transparent slot is shifted slightly and further exposure steps are performed with different UV intensity or exposure time. This is performed many times, so that after development, the pixel electrode surface is left with irregular stepped ridges on its surface topography. A further mask is then used to create microbumps on the edge surfaces, which are then heated to propagate the reflow. This provides a viewing area optimized for the DMSR pixel electrode. However, in the production of LCD displays, multiple UV exposure is very time consuming and expensive. In addition, standard photolithographic aligners used in AMLCD factories generally do not include equipment for multiple exposure shifts. Thus, this unique multiple exposure method disclosed in US Pat. No. 6,163,405 is impractical for use in mass production of LCD displays.

  Another method disclosed in US Pat. No. 6,163,405 uses a gray tone mask, also known as a halftone mask. This is a photomask having an area that exhibits at least one translucency for light. As a result, a certain intensity of ultraviolet light can be applied through this mask over a set exposure time to produce multiple exposure levels of the photosensitive material. For example, a substrate for an LCD covered with photosensitive material and subjected to a single UV exposure through a gray-tone mask, when developed, is the same as that created using the photolithography multiple exposure shift method Has multi-level surface topography.

  One method for producing a gray-tone photomask is to create a fine pattern of transmissive apertures on a mask that would otherwise be opaque and partially reduce the amount of UV transmission. Furthermore, since the light passing through the mask is diffracted and thus dispersed, a fairly uniform exposure is achieved when used to expose the photosensitive material. By changing the size of the aperture, various percentages of UV light can be passed through the mask. These types of gray-tone masks can be produced in almost any shape. However, their main drawback is that when very small shapes of less than 2 μm are required, for example when producing diffusely reflective pixel electrodes for LCDs, they are very expensive to produce That is. In addition, diffraction at the edge of a feature on the mask reduces the sharpness of the feature, limiting the accuracy of the mask. These disadvantages make the use of diffraction masks impractical for certain industrial applications.

  The present invention proposes a method for reducing costs associated with the production of AMLCD cell molding structures that use gray-tone photomasks with materials such as silicon-rich silicon nitride hydrogenated in photolithographic production processes. Silicon rich silicon nitride (SiNx) masks can be produced relatively inexpensively even when small shapes are required.

  According to one aspect of the present invention, a method of forming a molded structure on a device plate (eg, transistor plate) comprising applying a photosensitive layer to the plate and at least one region of semi-transmissive material. And forming a molded structure in the photosensitive layer in a photolithographic process using a gray-tone photomask, wherein the material has a certain degree of transparency depending on the optical band gap of the material. Is done.

  The present invention further provides a method for generating irregular surface topography for the diffusely reflective pixel electrode of the liquid crystal display using such a photomask in the photolithographic process. The surface topography for the diffusely reflective pixel electrode of the liquid crystal display has a number of thickness degrees.

  The material region used in the gray tone photomask is hydrogenated silicon rich silicon nitride SiNx: H, where x is less than 1.

  Advantageous features according to the invention are described in the claims. These and other features will be described, by way of example, in specific embodiments of the invention described below with reference to the accompanying drawings.

  FIGS. 1 a-1 e illustrate one embodiment of a method for producing a diffuse reflective pixel electrode for use in AMLCD using a SiNx gray tone mask. In this embodiment, the AMLCD incorporates microbumps without diffuse micro-gradient reflection (DMSR) features.

  FIG. 1a shows an active matrix liquid crystal display (AMLCD) device that incorporates a diffuse reflective TFT electrode whose manufacturing process is represented in FIGS. The liquid crystal 1 is interposed between the TFT plate 2 and the glass substrate 3. Further, in order to provide an array of red pixels, green pixels, and blue pixels, a color filter layer 4 arranged in a pattern of red regions, green regions, and blue regions is shown. The TFT 5 is switched by a row electrode and a column electrode (not shown).

  FIG. 1b is a cross-sectional view of a TFT pixel electrode plate 2 as used in AMLCD after a layer of photosensitive polymer 6 has been applied. The polymer is composed of a material such as polyimide, acrylic, or photoresist. In one example, the material used was a positive tone aqueous developable photosensitive HD-8001 polyimide as produced by HD Microsystems. This is applied using known methods such as spinning or screen printing. Also shown in FIG. 1b is a SiNx gray tone mask 7 utilized during the photolithographic stage in the production process. This mask is formed by depositing a translucent SiNx layer 8 and an opaque chrome layer 9 on an ultraviolet transmissive mask substrate 10. Since the mask region 10A is not covered with the layer 8 or 9, it passes ultraviolet light.

  The mask 7 is placed in alignment with the TFT plate and the ultraviolet light is directed in a direction through the TFT plate to expose the photosensitive polyimide coating 6 on the TFT plate 2. FIG. 1c represents this stage in the process, showing the TFT plate 2 with the exposed area 11 of polysilicon after UV irradiation. The area of polysilicon just below the chrome area of the mask is not exposed due to the obscured nature of chrome. These are marked as 0% Tr in the drawing and the UV transmission is shown as 0%. Areas of the photosensitive polyimide immediately below the UV transmissive area of the mask, such as area 10A, are fully exposed and those areas below SiNx area 8 are partially marked, for example, as 35% Tr. The amount of exposure depends on the optical properties of the SiNx used. This photolithographic process is used to define the microbumps 12 and vias 13 for connection to the TFT electrodes 5. In positive photolithography, the exposed photosensitive polyimide 6 with a certain thickness depending on the UV irradiation dose is then removed in the development stage.

  FIG. 1 d is a cross-sectional view of the TFT plate after the development stage of the photosensitive polyimide 6. The polyimide exposure area 11 has been removed, and the polyimide surface topography now represents the form of vias 13 for contact between the microbumps 12 and the pixel electrodes 5.

  FIG. 1e shows the TFT plate after the final stage of production. This plate is first heated to cause a reflow that rounds the microbumps 12, giving the microbumps the topography necessary for the diffusely reflective pixel electrode. Next, a highly reflective metal layer 14 such as aluminum or silver is applied to the surface of the TFT plate in a manner such as sputtering.

The SiNx gray tone mask is formed by plasma depositing SiN _x : H onto an ultraviolet transparent substrate such as a quartz plate. In one example, RF capacitively coupled plasma deposition was performed at 13.56 MHz, a temperature in the range of 200-350 degrees Celsius, and a pressure in the range of 50-200 Pascals. Other frequencies, temperatures and pressures can also be used. A preferred vapor deposition gas is a mixture of silane, ammonia, nitrogen and hydrogen, although other mixtures may be used. The proportion of nitrogen x in the deposited characteristic layer varies from 0.001 to 1.4, resulting in an increase in the material optical band gap from 1.7 eV to 6.0 eV. Preferably, the ratio x used is between 0.2 and 0.6 associated with a band gap of between 2.1 eV and 2.5 eV. FIG. 2 is a graph of the optical band gap Eopt shown by the layer of SiNx plasma deposited according to the ratio of NH ₃ (ammonia gas) to SiH ₄ (silane gas) used in the deposition process.

  By incorporating SiNx with a specific light band gap into the gray tone mask, a specific UV light transmission is observed. FIG. 3 is a graph showing the transmittance shown by the three types of SiNx layers A, B and C according to the wavelength of the ultraviolet rays. The optical band gap of SiNx in layer A and the optical band gap of layer B are 2.14 eV. The layer represented by C has an optical band gap of a combination of one A layer and one B layer. Typically, UV treatment uses g, h or i baselines of mercury light as shown in FIG.

  FIG. 4 is a graph showing the transmission characteristics of three SiNx layers D, E, and F, each deposited with increasing thickness, each having an optical band gap of 2.3 eV. The thickness of layer D is 60 nm, layer E is 66 nm, and layer F is 78 nm. Although the transmission characteristics of the SiNx layer are slightly affected, the influence of the thickness is considerably smaller than the optical band gap, particularly for ultraviolet light having an h-line wavelength. This contributes to the low-cost production of SiNx gray-tone masks because the high accuracy with respect to the deposition thickness is not critical.

  FIG. 5 shows one embodiment of a manufacturing process of a SiNx photomask as used in the present invention. In the first stage, plasma deposition on the UV transparent substrate 15 is used to form a first SiNx layer 16 having a thickness of 60 nm and an optical band gap of 2.14 eV. Using UV light h-rays, this layer has a UV transmittance of 35%, or 23% UV transmittance when used in combination with a SiNx layer with an optical band gap of 2.3 eV. Have Thus, the layer is then patterned using known techniques, leaving only areas where 35% or 25% transmission is required. FIG. 5a is a cross-sectional view of the mask after these first stages of SiNx photomask production.

  In a further stage of the mask production process, a chromium layer 17 is deposited on the substrate 15 and patterned. Chromium is left in areas of the mask where 0% UV transmission is required. Moreover, chromium is left in areas where 35% UV transmission is required, i.e. on the previously deposited SiNx layer 16. This is done so that the chromium layer 17 acts as a shield layer to the first SiNx layer 16 when a further SiNx layer is deposited. The resulting mask is shown in FIG.

  FIG. 5c is a cross-sectional view of the mask after deposition and patterning of a second SiNx layer 18 having a thickness of 60 nm and an optical band gap of 2.3 eV. This is left in the region of the mask where 23% or 54% transmission is required, with 23% being realized by this SiNx layer 18 combined with the first SiNx layer 16.

  FIG. 5 d is a cross-sectional view of the mask after the second patterning of the chromium layer 17. This is performed in order to irradiate a region where a transmittance of 35% is required, that is, a region where the first SiNx layer 16 has a constant volume. The mask is now complete, and in this example has five different transmission properties, 0%, 23%, 35%, 54% and 100% as shown in FIG. 5d.

  FIGS. 6a-6c show how to incorporate a SiNx photomask to produce DMSR (diffuse micro-gradient reflector) pixel electrodes for TFT AMLCDs. As already explained, the first stage relates to the application of the photosensitive material layer 19 to a previously prepared TFT plate 20. In this example, layer 19 is HD-8001 from HD Microsystems and is applied using a conventional spin coating technique of about 500-3000 rpm to produce a polyimide thickness of about 2 μm. A photomask 21 similar to the photomask of FIG. 5 is then placed in alignment with the TFT plate, and ultraviolet light is passed through the photomask to irradiate the photosensitive polyimide 19. This stage of the process is shown in FIG. 6a, where the exposed area 22 depends on the UV light transmission through the photomask 21. The layers on the photomask are chrome 17, a first SiNx layer 16 having a transmittance of 35%, and a second SiNx layer 18 having a transmittance of 54%. As mentioned above, the combination of the two types of SiNx layers provides 23% transmission. In this embodiment, the feature on the photomask that defines the micro bumps of the DMSR pixel is square when viewed from above, and has a width of about 2 μm. Each inclined region, such as the region of FIG. 6a, has a length of about 5 μm in this embodiment.

  FIG. 6b is a cross-sectional view of the TFT plate after development of the exposed polyimide and a further heating step to cause reflow. This provides a surface topography of the reflective pixel electrode that has rounded microbumps and has an inclined feature that gradually raises the bumps 23, 24, and 25. In the final stage of this embodiment, silver may be used, but the highly reflective aluminum layer 26 is applied to the TFT plate using a sputtering process. The resulting DMSR pixel electrode is shown in FIG.

  FIG. 7a represents a cross-sectional view of a DMSR pixel electrode at a stage of manufacture. A photolithographic exposure step has been performed, followed by development of the photosensitive polyimide. In this embodiment, four types of polyimide remain on the TFT plate 25 as represented by 28, 29, 30 and 31 at this time. A plan view of the pixel electrode 32 is shown in FIG. 7b and displays its layout. Each of the micro bumps 33 is a quadrangle in this embodiment, but other polygonal or circular shapes may be used. Further, a larger number of micro bumps 33 may be provided for each pixel 32 so as to provide a satisfactory LCD viewing area.

  From reading the above disclosure, other variations and modifications will be apparent to persons skilled in the art. Such variations and modifications are known in the design, manufacture and use of photomasks and include equivalent and other features used in place of or in addition to the features described herein. Including.

2 is a cross-sectional view of a TFT plate for a reflective LCD display at various stages of the process used to define a diffuse reflective surface topography. FIG. 2 is a cross-sectional view of a TFT plate for a reflective LCD display at various stages of the process used to define a diffuse reflective surface topography. FIG. 2 is a cross-sectional view of a TFT plate for a reflective LCD display at various stages of the process used to define a diffuse reflective surface topography. FIG. 2 is a cross-sectional view of a TFT plate for a reflective LCD display at various stages of the process used to define a diffuse reflective surface topography. FIG. 2 is a cross-sectional view of a TFT plate for a reflective LCD display at various stages of the process used to define a diffuse reflective surface topography. FIG. FIG. 6 is a graph plotting the optical band gap of a SiNx layer with various NH3 / SiH4 gas ratios as used for the production of SiNx layers. FIG. 5 is a graph in which the transmission characteristics of three types of configurations A, B and C of SiNx, each having a different optical band gap as used in a photomask, are plotted according to the wavelength of light used. It is a graph in which the transmittances of three types of thicknesses D, E, and F of SiNx each having an optical band gap of 2.3 eV are plotted according to the wavelength of light used. FIG. 3 is a cross-sectional view of a SiNx photomask at various stages in the manufacture of the SiNx photomask. FIG. 3 is a cross-sectional view of a SiNx photomask at various stages of SiNx photomask manufacture. FIG. 3 is a cross-sectional view of a SiNx photomask at various stages in the manufacture of the SiNx photomask. FIG. 3 is a cross-sectional view of a SiNx photomask at various stages in the manufacture of the SiNx photomask. FIG. 6 is a diagram illustrating a method of forming a micro bump including an inclined shape on a TFT AMLCD pixel electrode using a SiNx photomask. It is sectional drawing of the TFT plate after formation of the microbump which has an inclined shape on the surface. It is a top view of the TFT plate after formation of the microbump which has an inclined shape on the surface.

Claims (11)

A method of forming a molded structure on a device plate, comprising:
Applying a photosensitive layer to the plate;
Forming the molded structure in the photosensitive layer in a photolithographic process using a gray-scale photomask with a region of at least one translucent material having a transparency depending on the optical band gap of the material;
A method involving that. The region of the material used for the gray-tone photomask is hydrogenated silicon rich silicon nitride SiN _x : H, where x is less than 1, 2. Method. Before forming the molded structure in the liquid crystal display cell,
Depositing a layer of the semi-transmissive material to form a region of the semi-transmissive material on the UV transmissive substrate;
Patterning the translucent material;
Depositing a layer of UV opaque material on the substrate;
Patterning the layer of UV opaque material,
The method according to claim 1, further comprising forming the photomask. In order to form a second region of translucent material on the UV transmissive substrate, a layer of a second translucent material having a different transmission from the first material is deposited, depending on the optical band gap of the material. ,
Patterning the second translucent material,
The method of claim 3.   5. A method according to claim 4, characterized in that the layer of UV-impermeable material is patterned again.   6. A method according to claim 3, 4 or 5, characterized in that the UV opaque material is Cr.   7. The photomask according to claim 1, wherein the photomask is used in the photolithographic process to generate irregular surface topography for a diffuse reflective pixel electrode of a liquid crystal display. the method of.   8. The method of claim 7, wherein the surface topography for the diffusely reflective pixel electrode of the liquid crystal display has multiple thickness levels.   9. A method according to any one of the preceding claims, characterized in forming an AMLCD comprising the device plate.   A liquid crystal display device manufactured by the method according to claim 1.   A mask made for use in the method of claim 1.

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